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  <div class="question_difficulty">
   难度：Medium
  </div>
  <div>
   <h1 class="question_title">
    930. All Possible Full Binary Trees
   </h1>
   <p>
    A
    <em>
     full binary tree
    </em>
    &nbsp;is a binary tree where each node has exactly 0 or 2&nbsp;children.
   </p>
   <p>
    Return a list of all possible full binary trees with
    <code>
     N
    </code>
    nodes.&nbsp; Each element of the answer is the root node of one possible tree.
   </p>
   <p>
    Each
    <code>
     node
    </code>
    of each&nbsp;tree in the answer
    <strong>
     must
    </strong>
    have
    <code>
     node.val = 0
    </code>
    .
   </p>
   <p>
    You may return the final list of trees in any order.
   </p>
   <p>
    &nbsp;
   </p>
   <p>
    <strong>
     Example 1:
    </strong>
   </p>
   <pre>
<strong>Input: </strong><span id="example-input-1-1">7</span>
<strong>Output: </strong><span id="example-output-1">[[0,0,0,null,null,0,0,null,null,0,0],[0,0,0,null,null,0,0,0,0],[0,0,0,0,0,0,0],[0,0,0,0,0,null,null,null,null,0,0],[0,0,0,0,0,null,null,0,0]]</span>
<strong>Explanation:</strong>
<img alt="" src="https://s3-lc-upload.s3.amazonaws.com/uploads/2018/08/22/fivetrees.png" style="width: 700px; height: 400px;">
</pre>
   <p>
    &nbsp;
   </p>
   <p>
    <strong>
     Note:
    </strong>
   </p>
   <ul>
    <li>
     <code>
      1 &lt;= N &lt;= 20
     </code>
    </li>
   </ul>
  </div>
  <div>
   <h1 class="question_title">
    930. 所有可能的满二叉树
   </h1>
   <p>
    <em>
     满二叉树
    </em>
    是一类二叉树，其中每个结点恰好有 0 或 2 个子结点。
   </p>
   <p>
    返回包含
    <code>
     N
    </code>
    个结点的所有可能满二叉树的列表。 答案的每个元素都是一个可能树的根结点。
   </p>
   <p>
    答案中每个树的每个
    <code>
     结点
    </code>
    都
    <strong>
     必须
    </strong>
    有
    <code>
     node.val=0
    </code>
    。
   </p>
   <p>
    你可以按任何顺序返回树的最终列表。
   </p>
   <p>
    &nbsp;
   </p>
   <p>
    <strong>
     示例：
    </strong>
   </p>
   <pre><strong>输入：</strong>7
<strong>输出：</strong>[[0,0,0,null,null,0,0,null,null,0,0],[0,0,0,null,null,0,0,0,0],[0,0,0,0,0,0,0],[0,0,0,0,0,null,null,null,null,0,0],[0,0,0,0,0,null,null,0,0]]
<strong>解释：</strong>
<img alt="" src="https://aliyun-lc-upload.oss-cn-hangzhou.aliyuncs.com/aliyun-lc-upload/uploads/2018/08/24/fivetrees.png" style="height: 400px; width: 700px;">
</pre>
   <p>
    &nbsp;
   </p>
   <p>
    <strong>
     提示：
    </strong>
   </p>
   <ul>
    <li>
     <code>
      1 &lt;= N &lt;= 20
     </code>
    </li>
   </ul>
  </div>
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